The present invention relates generally to biomedical electrodes attached to the body for electrical monitoring or stimulating purposes. More particularly, it relates to a disposable biomedical electrode and a corresponding connector that provide a secure, high-integrity, mechanical and electrical interface between a person's skin and a medical instrument.
It is well known that physiological operation of the human heart produces electrical activity that manifests itself in a measurable electrical parameter on the human skin. This electrical activity can be recorded by an electrocardiograph which, by definition, is an instrument that records electric potentials associated with electric currents that traverse the heart. It is also well known that physiological functioning of the brain exhibits electrical activity. To this end, an electroencephalograph is an instrument that records the brain's electrical activity.
Electrical activity of the heart is presented for observation and study by way of an electrocardiogram (ECG), which is a graphical record of the activity, typically the amplitude of the electrical parameter (e.g., voltage) versus time. Electrocardiography is the well-developed science of studying ECGs for medical diagnostic purposes. Electrocardiography is used in a variety of medical procedures to monitor the activity, and diagnose the health, of the human heart.
Further, electromyography is the study of muscular contractions resulting from electrical voltages applied to specific muscle nerves. For example, electromyography can be used when a person is anesthetized in preparation for an operation. Here, specific nerves are stimulated with electricity and simultaneously monitored to see if the anesthetic is working.
In order to sense the electrical signal that is manifested on the human skin, or to provide muscular stimulation, an electrode is typically employed. A sensed electrical signal is transported by an electrical wire from the electrode to the electrocardiograph. The wire is removably attached to the electrode by connector means. A similar system may be used instead for therapeutic electrical stimulation of the muscles and/or nerves. In such instance, the electrocardiograph can be replaced by an electrical stimulating instrument, such as a defibrillator, that transmits electrical current into the body through electrodes. This system may also be used, for example, in electroconvulsive therapy. See U.S. Pat. Nos. 4,736,752 and 5,038,796. In either system, the critical connections are the interface points between the electrode and the human skin, and also between the electrode and the wire cabling. The overall electrical path extends between the human skin, electrode, connector, wire cabling, and medical instrument.
It is known in the early art of electrodes for monitoring or stimulating purposes to use an electrode having a conductive metal surface applied to the skin. The electrodes are held in place, for example, by belts or suction cups. However, these means, because they are inherently uncomfortable, do not lend themselves to long-term usage. An electrically conductive media, such as paste, cream or gel, is applied between the electrode's metal sensing surface and skin to insure a continuous connection therebetween; ideally, across the entire conductive surface area of the electrode. As a rule, direct contacting of an electrode with the skin does not provide sufficient electroconductivity therebetween. The conductive media reduces the air gaps between the electrode and skin, thereby reducing both the amount of impedance of the electrical circuit and any undesirable artifacts or noise in the sensed signal. Such noise can reduce the quality of the signal for diagnostic purposes.
However, this approach suffers from numerous drawbacks, including the fact that the conductive cream or gel is messy to work with and often leaves an undesirable residue. Also, the electrode is not suited for long-term usage. Further, this approach is relatively costly to implement.
It is known in the more recent art of electrodes to use a less-expensive, disposable biomedical electrode. This electrode may comprise a low profile, somewhat flexible pad or substrate having an adhesive surface that is applied directly to the human skin. A portion or all of the adhesive surface may utilize an electrically-conductive gel (e.g., a conductive polymer or hydrogel) that interfaces directly with the skin. The gel is contained in a pad or substrate, typically by impregnating the hydrogel within a porous matrix, such as a woven or non-woven fabric, for example, rayon. Alternately, the hydrogel without a matrix may be disposed within a cavity formed in the pad or body of the electrode or used as a surface coating. See U.S. Pat. No. 4,722,761. The hydrogel is often lightly adherent to the skin, but is sufficiently cohesive throughout so that the pad is easily removed from the skin without leaving any undesirable gel residue thereon when the pad is removed. The tackiness of the hydrogel can be controlled by the amount of cross-linking component in the gel. The gel allows a small amount of relative movement of the electrode with respect to the skin, and is typically able to withstand perspiration, humidity and changes in body temperature without losing its desirable properties. The opposite surface of the pad is attached, usually by lamination, to a conductive metal or conductive circuit that is in physical contact with the hydrogel. See U.S. Pat. Nos. 3,998,215 and 4,515,212. In the alternative, the interfacing element between the conductive metal or conductive circuit and the skin may be comprised of a sponge saturated with an electrolyte solution.
However, the term "hydrogel" usually refers to a gel having a high water content. Thus, the hydrogel will remain solid and in gel form only as long as its water content is retained. Electrolytes also evaporate over time. To prevent evaporation of the water in the hydrogel (which renders the electrode useless), the electrode may be sealed in an aluminum foil package that is impermeable to the ambient environment. See U.S. Pat. No. 3,998,215. Or, the hydrogel may be enclosed within a peelable release paper. See U.S. Pat. No. 5,120,544. This has the effect of increasing the shelf-life of the electrode, but increases the overall cost to manufacture.
Some additional problems encountered with known electrodes include the fact that electrodes with sponges and gel cups tend to be bulky and inflexible, making the electrode uncomfortable and/or undesirably conspicuous. Lack of flexibility can cause the electrode to pull away from the skin, thereby causing discontinuity of the electrical signal. Also, lack of flexibility may cause premature failure and patient discomfort.
Disposable electrodes are typically available with two types of connectors. A first type is referred to as a "snap" connector electrode. The snap connector comprises an electrically-conductive male extension portion of the electrode that protrudes above the top of the upper surface of the electrode. A corresponding female receptacle is then snapped onto the male extension. The female receptacle is in electrical connection with the electrocardiograph by means of the electrical wiring. See U.S. Pat. Nos. 3,998,215; 3,895,635; 3,696,807; 4,029,086; 3,085,577 and 3,830,229. The snap conductor or fastener is of a two-part construction, and either totally or partially comprises silver, nickel, stainless steel or other conductive metals or metalized plastic. As such, the fastener is a relatively expensive part of the overall electrode. Also, the snap fastener is of considerable mass relative to the remainder of the electrode. Thus, any patient movement may cause the electrode to move relative to the skin of that patient, especially such movements that produce tension in the wire cabling.
A second type of electrode is known as the "tab"-type electrode that has a lateral planar extension of the conductive electrode. The extension is the "tab" to which an alligator clip is usually attached. See U.S. Pat. Nos. 4,852,571; 4,890,622; 4,657,023 and 4,674,512. The wire connection to the electrocardiograph is attached to the alligator-type clip.
Problems with the tab-type electrode include the fact that while the electrode is made to be disposable, the corresponding connector is not. Over time, the gripping action of the clip-on alligator-type connectors tends to weaken. Such weakening degrades the electrical contact between the tab portion of the electrode and the connector, resulting in a degradation of the transmission of the signal from the electrode. Further, if the tab is located on the edge of the electrode, the alligator clip exerts a force on the tab, especially during a patient movement that tugs on the clip, that tends to lift the electrode off the skin, thereby degrading the transmission of the signal from the electrode.
It is to be understood that other variations on the above-described two types of electrodes are well-known.
Accordingly, it is a primary object of the present invention to provide a biomedical electrode system that includes a disposable electrode and corresponding connector that together provide a long-lasting and reliable, high-integrity mechanical and electrical connection between the human skin and a medical instrument.
It is a general object of the present invention to provide a stationary and high-integrity electrical interface between a conductive tab portion of a disposable biomedical electrode and a conductor component portion of a corresponding connector.
It is a further object of the present invention to provide a disposable, inexpensive, flexible, mass-producible electrode that is of relatively thin, flat, and low-profile construction.
It is yet another object of the present invention to provide a biomedical electrode that eliminates the hard protrusions of studs or gel cups in the rigid construction of prior art electrodes.
It is still another object of the present invention to provide a biomedical electrode that is radio translucent and that rapidly dissipates defibrillation charges.
It is still another object of the present invention to provide a biomedical electrode that allows for patient movement and cable strain relief through the flexible characteristics of the electrode.
The above and other objects and advantages of the present invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.